全文获取类型
收费全文 | 21758篇 |
免费 | 1861篇 |
国内免费 | 987篇 |
专业分类
电工技术 | 1211篇 |
综合类 | 2430篇 |
化学工业 | 1870篇 |
金属工艺 | 2130篇 |
机械仪表 | 4140篇 |
建筑科学 | 2844篇 |
矿业工程 | 919篇 |
能源动力 | 394篇 |
轻工业 | 760篇 |
水利工程 | 594篇 |
石油天然气 | 724篇 |
武器工业 | 318篇 |
无线电 | 932篇 |
一般工业技术 | 2882篇 |
冶金工业 | 792篇 |
原子能技术 | 178篇 |
自动化技术 | 1488篇 |
出版年
2024年 | 85篇 |
2023年 | 238篇 |
2022年 | 451篇 |
2021年 | 579篇 |
2020年 | 622篇 |
2019年 | 545篇 |
2018年 | 530篇 |
2017年 | 744篇 |
2016年 | 824篇 |
2015年 | 892篇 |
2014年 | 1209篇 |
2013年 | 1290篇 |
2012年 | 1424篇 |
2011年 | 1617篇 |
2010年 | 1185篇 |
2009年 | 1237篇 |
2008年 | 1192篇 |
2007年 | 1523篇 |
2006年 | 1378篇 |
2005年 | 1133篇 |
2004年 | 951篇 |
2003年 | 855篇 |
2002年 | 684篇 |
2001年 | 585篇 |
2000年 | 533篇 |
1999年 | 484篇 |
1998年 | 304篇 |
1997年 | 349篇 |
1996年 | 271篇 |
1995年 | 230篇 |
1994年 | 159篇 |
1993年 | 106篇 |
1992年 | 83篇 |
1991年 | 70篇 |
1990年 | 54篇 |
1989年 | 57篇 |
1988年 | 56篇 |
1987年 | 24篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1956年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
AFM-based single abrasive abrasion process is widely employed in the surface micro/nanomachining for fabrication of structures at the nanometer scale. The wear depth and roughness are significantly important in the application of these structures. To study effects of scratching directions on the wear depth and roughness within the wear mark, single groove scratching test and wear test on the surface of polished single crystal silicon were carried out using AFM with a pyramidal diamond tip. Single groove scratching tests indicated that tip geometry leads to different removal states such as cutting and plowing. At the same load, deeper wear depth and rougher surface were produced by using the scratching direction perpendicular to the long axis of the cantilever rather than parallel to the long axis of the cantilever. Surface roughness decreases with respect to the feed scratching perpendicular to the long axis of the cantilever, whereas while scratching along the long axis of the cantilever, the surface roughness is rougher at the small feed. This is attributed to the different stiffness of the cantilever along different scratching directions and different removal states between the tip and sample. 相似文献
992.
五轴数控加工中心的切削稳定性是影响其切削效率的重要因素。在阐述切削稳定性预测过程的基础上,对国内外学者在切削稳定性分析方面的研究成果进行了综合介绍。重点论述了切削力的建模方法以及切削力系数辨识方法,并对切削稳定性仿真方法进行了归纳。分析了在切削稳定性分析研究方面存在的不足,并提出今后稳定性分析的发展方向。 相似文献
993.
994.
针对某轿车后悬架减振器出现的异响问题,进行阻尼器高频振动试验,对位移-阻尼力图形分析确定异响由复原阀系造成,通过对复原阀系进行结构设计优化,改善位移-阻尼力图形,最后将改善后的复原阀系装配于新的减振器进行噪声台架测试验证和整车道路试验验证,结果表明,改进后的减振器异响消除。 相似文献
995.
多方向宽频磁电式振动能量采集器 总被引:4,自引:0,他引:4
针对目前振动能量采集器只能拾取环境振动中一个方向的能量,以及响应频带较窄的问题,提出并设计了一种由弹性圆柱悬臂梁、环形磁路和复合磁电换能器组成的多方向宽频带振动能量采集器.圆柱悬臂梁具有在其横截面内沿任意方向振动的特性,同时,借助磁力耦合,使任意方向振动具有非线性的特点,从而采集器实现多方向宽频带振动能量拾取.理论推导了磁力作用下圆柱悬臂梁的非线性动力学方程,以及电压输出模型;借助磁场分析软件Ansoft Maxwell分析了矩形、圆形和环形永磁铁分别组成3种磁路的磁场分布,研究了不同磁路中磁力、磁场强度及其变化量等因素对动力学方程和电压输出的影响,为获得更优性能的采集器提供了设计依据.实验结果表明:在5.88 m/s2的加速度下,具有环形磁路的采集器能够拾取0°~ 180°多方向的振动能量,各个方向响应频带宽度达到4.4~5.6Hz;负载电阻为3 MΩ时,采集器输出0.5 mW的最大功率. 相似文献
996.
利用拉格朗日(Lagrange)方程建立了非稳态油膜力的转子-定子-轴承系统碰摩故障的力学模型,应用数值分析对其进行研究,得出转子系统在激励频率作为唯一控制参数时系统的轴心轨迹图和分岔图;对该系统响应的非线性行为和故障机理进行分析,从而为该类转子系统故障诊断和系统的安全运行提供理论依据.研究结果表明,当激励频率作为唯一控制参数时,系统存在周期运动、拟周期运动和混沌运动等丰富的非线性现象. 相似文献
997.
There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale. 相似文献
998.
The optimisation of high-performance cutting (HPC) processes under technological and economical aspects often proves to be extremely difficult due to the appearance of process instabilities, so-called “chatter”. The identification of ideal process parameters often involves the systematic testing with varied cutting parameters. Simulation of the process stability offers a less costly way of optimising processes prior to production. However, the predictions for the stability of high performance milling processes exhibit great deviation from experimental results. The objective is to analyse and to prevent errors within the simulation methods to make stability simulation a reliable tool in process planning. In order to improve the quality of stability simulation, the interacting Systems “Machine Tool” and “Cutting Process” are analysed individually. Methods for the coupled simulation of both systems are implemented to identify stable working conditions. As a result of this work, a time domain simulation environment for the investigation of high performance milling operations is presented. It considers the complex behaviour of the cutting process as well as the speed dependent machine tool dynamics. Cutting tests have been conducted to verify the benefit of the enhanced simulation method. 相似文献
999.
ABSTRACTA prediction model of cutting force for milling multidirectional laminate of carbon fiber reinforced polymer (CFRP) composites was developed in this article by using an analytical approach. In the predictive model, an equivalent uniform chip thickness was used in the case of orthogonal plane cutting, and the average specific cutting energy was taken as an empirical function of equivalent chip thickness and fiber orientation angle. The parameters in the model were determined by the experimental data. Then, the analytical model of cutting force prediction was validated by the experimental data of multidirectional CFRP laminates, which shows the good reliability of the model established. Furthermore, the cutting force component of flank contact force was correlated with the surface roughness of workpiece and the flank wear of tool in milling UD-CFRP composites. It was found that surface quality as well as flank wear has a co-incident varying trend with the flank contact force, as confirmed by the observations of the machined surfaces and tool wear at different fiber orientations. So, it can be known that low flank contact force be required to reduce surface damage and flank wear. 相似文献
1000.